Increasing the neutralino relic abundance with slepton coannihilations: consequences forindirect dark matter detection

Abstract

We point out that if the lightest supersymmetric particle (LSP) is a higgsino- or wino-likeneutralino, the net effect of coannihilations with sleptons is to increase the relic abundance,rather than producing the usual suppression, which takes place if the LSP is bino-like.The reason for the enhancement lies in the effective thermally averaged crosssection at freeze-out: sleptons annihilate (and coannihilate) less efficiently than theneutralino(s)–chargino system, and therefore slepton coannihilations effectively act asparasite degrees of freedom at freeze-out. Henceforth, the thermal relic abundance ofLSPs corresponds to the cold dark matter abundance for smaller values of theLSP mass, and larger values of the neutralino pair annihilation cross section. Inturn, at a given thermal neutralino relic abundance, this implies larger indirectdetection rates, as a result of an increase in the fluxes of antimatter, gammarays and neutrinos from the Sun originating from neutralino pair annihilations.